The unreacted methacrylate groups on the surface of conventional composites and microfilled composites were studied by means of multiple internal reflection infrared spectroscopy. The influences of polymerization time, temperature, and the effect of polishing were studied. We also attempted to relate the results of some mechanical tests to the degree of chemical unsaturation measured in the different resins. All surface treatment and manipulative variables caused a decrease in double bond content and interfacial bond strength.

Unreacted Methacrylate Groups on the Surfaces of Composite Resins

Statement of Problem: An often-debated issue still exists concerning implant impression techniques, whether to splint impression copings. Different configurations are available for these copings for a variety of manufacturers' implant systems. Purpose: This study evaluated and compared 4 impression techniques in terms of their dimensional accuracy to reproduce implant positions on working casts. Material and Methods: A master model was designed to simulate a clinical situation. Impressions were made using 4 techniques: (1) tapered impression copings not splinted; (2) squared impression copings not splinted; (3) squared impression copings splinted with autopolymerizing acrylic resin; and (4) squared impression copings with a lateral extension on one side not splinted. Reference points machined onto the master model and onto special healing abutments were compared after abutments were transferred to casts using the 4 techniques. Measurements were made using a Reflex microscope, capable of recording in the x-, y-, and z-dimensions. Results: The dimensional accuracy was high and, although statistically significant ( P =.022; power > 80%), a maximum distortion difference of only 0.31% was registered. Conclusion: The dimensional accuracy of all the techniques was exceptional and the observed differences can be regarded as clinically negligible. (J Prosthet Dent 2000;83:555-61.)

Evaluation of impression accuracy for osseointegrated implant supported superstructures

Impression trays were fabricated providing 2, 4, and 6 mm spaces to determine the stability and accuracy of nine elastomeric impression materials on a simulated full crown preparation steel die. The interface space of 2 mm produced the most accurate impressions for all of the materials tested. All impression materials except one fell within the revised American Dental Association Specifications. The clinical-type tests, using castings on dies poured from these materials, corroborated the acceptance of those materials and techniques exhibiting the least dimensional change.

Elastomeric impression materials: Effect of bulk on accuracy

Both addition and condensation silicones produced stone dies that were larger in diameter and shorter in height than the tooth preparation. For both materials, there was little change in the distance between stone die preparations compared with the standard. The most significant difference between types of silicone was that condensation silicones produced significantly shorter dies (-0.24% to -0.37%) than addition silicones (-0.08%). Among addition silicones, Cinch produced more than twice as much vertical change (-0.16%) than the other three products (-0.06%). Since castings made from a short die will not seat completely on the prepared tooth, these results support the use of three of the four addition silicones tested. The same accuracy of impressions was achieved for all techniques (that is, putty/wash, single mix, and double mix) when addition silicones were used, whereas the putty/wash technique produced the most accurate dies for the condensation silicones. The custom tray produced dies that were much more accurate in vertical dimensions (-0.03%) than the stock trays (-0.15% to -0.21%). Thus the custom tray is the impression tray of choice, even for addition silicones, which produce relatively little polymerization shrinkage and are dimensionally stable.

Accuracy of addition silicones as a function of technique.

Interfacial bond strengths of light-activated composites were measured as a function of age using a transverse strength test. Bond strength between layers decreased with the age of the initial layer and reflected the setting curves of the composites. The highly-filled composites exhibited the greatest bond strengths. Uncut surfaces provided a better substrate for bonding than did ground surfaces. Use of a bonding agent on both uncut and ground surfaces improved bond strengths. Mean repair strengths of light-activated composites were similar to those of selfcuring composites. Composites with ground surfaces aged for one wk had mean repair strengths 27% of the cohesive strength without bonding agent and 48% with bonding agent.

Build-up and Repair of Light-cured Composites: Bond Strength

Summary A specific test was used to determine the accuracy of the highly filled silicone impression materials. They proved to be as accurate as the other standard impression materials tested. Two of the three highly filled silicone systems had the advantage of showing the lowest variability of accuracy. This study supports the use of the Class IV silicones for dental duplication procedures when such materials are used in conjunction with a corrective wash. This procedure obviates the need for making a custom impression tray.

The accuracy of highly filled elastomeric impression materials

This investigation evaluated preceramic and postceramic soldering procedures. Three gap spaces and two soldering methods were evaluated. Wider gaps produced stronger joints. The strongest joints were achieved by using wider gaps and the oven soldering technique. Very wide gaps (0.76 mm.) are not recommended because of possible distortion through excessive solder shrinkage. However, in practice, many solder joints exceed the 0.31 mm. recommended minimum; these joints will not show decreased strength.

Preceramic and postceramic solder joints.

Strength parameters of composite resins.

Silicone as a denture mold liner

A pilot study to investigate the effect of alumina-coated subperiosteal implants is reported. Initial clinical results are encouraging; there is evidence to indicate that a direct attachment occurs to the alumina surface. Histologic evidence will be reported at a later date. Further investigation studying the effect of other coatings, as well as different pore sizes, on the success of subperiosteal implants is planned.

M.H. Reisbick

Papers

The accuracy of highly filled elastomeric impression materials

Preceramic and postceramic solder joints.

Strength parameters of composite resins.

Silicone as a denture mold liner

Ceramic-coated subperiosteal implants. Part I. A pilot study